CONTEXT: Sarcomatous pulmonary neoplasms are a rare and diagnostically challenging group of tumors. Primary pulmonary sarcomas must be distinguished from the more frequent occurrence of sarcoma metastatic to the lung, primary pulmonary sarcomatoid carcinoma, and diffuse malignant mesothelioma involving the lung. In current practice, the general availability of ancillary diagnostic techniques, such as immunohistochemistry and molecular analysis, can reliably classify many sarcomatoid lesions. OBJECTIVE: To review the literature and report on additional primary material about the application of immunohistochemistry and molecular analysis in the differential diagnosis pulmonary sarcomatous neoplasms. DATA SOURCES: Literature review of relevant articles indexed in PubMed (National Library of Medicine) between 1961 and 2007 and primary material from the author's institution. CONCLUSIONS: This review discusses specific criteria for the diagnosis of primary lung sarcomas and offers a practical approach to excluding other sarcoma-like lesions involving the lung. The pathologist has an essential role in evaluating these tumors and will often be the first to suggest an unusual, alternative diagnosis, which may have significant implications for patient care, therapy, and prognosis.